U.S. patent number 3,891,408 [Application Number 05/386,718] was granted by the patent office on 1975-06-24 for zirconia-alumina abrasive grain and grinding tools.
This patent grant is currently assigned to Norton Company. Invention is credited to Robert A. Rowse, George R. Watson.
United States Patent |
3,891,408 |
Rowse , et al. |
June 24, 1975 |
Zirconia-alumina abrasive grain and grinding tools
Abstract
Very rapid crystallization of eutectic and neareutectic molten
mixtures of aluminum oxide and zirconium oxide, followed by
crushing of the solidified melt, results in abrasive grits of very
high strength combined with highly desirable microfracture
properties. The zirconium oxide in the material is in the form of
rods (or platelets) which, on the average, are less than 3000
angstroms in diameter, and preferably at least 25%, by weight, of
the zirconium oxide is in the tetragonal crystal form. The
solidified melt is made up of cells or colonies typically 40
microns or less across their width. Groups of cells having
identical orientation of microstructure form grains which typically
include from 2 to 100 or more cells or colonies. In crushing, the
material fractures along grain boundaries and cell boundaries.
Grinding improvement in excess of 100% of prior art standards is
shown in tests of coated abrasive products employing the crushed
abrasive material in typical applications and substantial
improvement in bonded abrasive products.
Inventors: |
Rowse; Robert A. (Shrewsbury,
MA), Watson; George R. (Chippawa, CA) |
Assignee: |
Norton Company (Worcester,
MA)
|
Family
ID: |
26964485 |
Appl.
No.: |
05/386,718 |
Filed: |
August 8, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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287489 |
Sep 8, 1972 |
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249204 |
May 1, 1972 |
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149837 |
Jun 3, 1971 |
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Current U.S.
Class: |
51/295; 51/298;
51/309; 501/105 |
Current CPC
Class: |
C04B
35/6261 (20130101); C04B 35/117 (20130101); C04B
35/62655 (20130101); C04B 35/109 (20130101); C04B
35/653 (20130101); C09K 3/1427 (20130101); C04B
2235/6565 (20130101); C04B 2235/72 (20130101); C04B
2235/3232 (20130101); C04B 2235/3206 (20130101); C04B
2235/3208 (20130101); C04B 2235/765 (20130101); C04B
2235/76 (20130101); C04B 2235/785 (20130101); C04B
2235/3272 (20130101); C04B 2235/3201 (20130101); C04B
2235/3418 (20130101) |
Current International
Class: |
C09K
3/14 (20060101); B24D 003/28 (); C09C 001/68 ();
C09K 003/14 () |
Field of
Search: |
;51/295,309,298
;106/57,65 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Arnold; Donald J.
Attorney, Agent or Firm: Hayes; Oliver W.
Parent Case Text
BACKGROUND OF THE INVENTION
The present application is a continuation-in-part of prior
copending application Ser. No. 287,489 filed Sept. 8, 1972, which
in turn was a continuation-in-part of applications Ser. No.
249,204, filed May 1, 1972 and Ser. No. 149,837, filed June 3, 1971
all now abandoned.
Claims
What is claimed is:
1. Abrasive grits consisting essentially of co-fused
alumina-zirconia, said alumina-zirconia abrasive having been
solidified from the molten state at least as rapdily as is
accomplished by casting molten alumina-zirconia abrasive into a
mold filled with 13/4 inch diameter cast iron balls said
alumina-zirconia being predominantly in the form of oriented
eutectic colonies associated together as grains within said grits,
the zirconia in said colonies being in the form of rods and/or
platelets, the maximum average rod spacing and platelet spacing
being 4000A, as measured at the colony centers by the random
intercept technique, and the maximum average size of primary
alumina or zirconia crystals, if any are present, being less than
50 microns, the zirconia content of the abrasive being from 35 to
50%, said abrasive grits having the characteristic that they will
fracture along and across colony boundaries when subjected to
grinding action while partially embedded in a cured thermoset
resin, the fracture providing striated or columnar surfaces
generally parallel to the long axes of the colonies and stepped
fracture surfaces across said long axes.
2. A coated abrasive comprising a flexible backing member having
adhesively bonded thereto abrasive grits consisting essentially of
co-fused alumina-zirconia, said alumina-zirconia abrasive having
been solidified from the molten state at least as rapidly as is
accomplished by casting molten alumina-zirconia abrasive into a
mold filled with 1 3/4 inch diameter cast iron balls said
alumina-zirconia being in the form of oriented eutectic colonies
associated together as grains within said grits, the zirconia in
said colonies being in the form of rods and/or platelets, the
maximum average rod spacing and platelet spacing being 4000A, as
measured at the colony centers by the random intercept technique,
and the maximum average size of primary alumina or zirconia
crystals, if any are present, being less than 50 microns, the
zirconia content of the abrasive being from 35 to 50%, the average
ratio of the maximum to minimum dimension of the abrasive grits is
at least 1.2 to 1, the adhesive bond being sufficiently strong to
hold the alumina-zirconia grits to permit fracture thereof during
grinding with creation of new cutting edges on the individual grits
as the result of the fracture, the fracture providing striated or
columnar surfaces generally parallel to the long axes of the
colonies and stepped fracture surfaces across said long axes.
3. A grinding wheel formed of abrasive grits held in an adhesive
bond, the majority of said abrasive grits consisting essentially of
co-fused alumina-zirconia, said alumina-zirconia abrasive having
been solidified from the molten state at least as rapidly as is
accomplished by casting molten alumina-zirconia abrasive into a
mold filled with 1 3/4 inch diameter cast iron balls said
alumina-zirconia being in the form of oriented eutectic colonies
associated together as grains within said grits, the zirconia in
said colonies being in the form of rods and platelets, the maximum
average rod spacing and platelet spacing being 4000A, as measured
at colony centers by the random intercept technique, and the
maximum average size of primary alumina or zirconia crystals, if
any are present, being less than 50 microns, the zirconia content
of the abrasive being from 35 to 50%, the adhesive bond being
sufficiently strong to hold the alumina-zirconia grits to permit
fracture thereof during grinding with creation of new cutting edges
on the individual grits as the result of the fracture.
4. Abrasive grits as in claim 1 in which at least 25% of the
zirconia is in the tetragonal crystal form.
5. A coated abrasive as in claim 2 in which at least 25% of the
zirconia in the abrasive is in the tetragonal crystal form.
6. Abrasive grits as in claim 1 including, along colony boundaries,
impurities selected from the group consisting of metals and
reduction products of metal oxides, and mixtures thereof.
7. A coated abrasive as in claim 2 in which the abrasive grits
include, along colony boundaries reduction products of the oxides
of metals contained in the abrasive composition.
8. A coated abrasive as in claim 2 in which at least 50% of the
alumina-zirconia abrasive grits exhibit a pseudo-hackly
fracture.
9. A coated abrasive as in claim 2 in which at least 50% of the
alumina-zirconia abrasive grits exhibit an all eutectic structure,
that is with no apparent primary alumina or primary zirconia
crystallization when polished sections of the grits are examined
under a microscope.
Description
This is an improvement in the fused alloy-type alumina-zirconia
abrasive materials which have come into commercial use since about
1960.
U.S. Pat. No. 3,181,939 discloses the rapid crystallization of
melts of alumina and zirconia, containing from 10 to 60%, by
weight, of zirconia. The eutectic composition is reported to occur
at 41% zirconia, by weight, (Schmid and Viechnicki, Journal of
Materials Science 5 (1970) pp. 470 to 473) and can very somewhat
due to impurities. We believe the more correct value is about 43%
zirconia. The patent teaches rapidly cooling melts by casting into
molds of from 25 to 300 pound capacity. The solidified product is
crushed to produce abrasive grits which have been found suitable
for snagging (rough grinding) applications when bonded in resinoid
grinding wheels. Other alumina-zirconia abrasives commercially
offerred for grinding wheels included "ZM Lionite," AZ 40 and R 81.
None of these abrasives had all of the improved properties of the
abrasive materials of this present invention.
U.S. application Ser. No. 814,162, filed Apr. 7, 1969, (of Quinan
and Supkis), discloses the use in some coated abrasive applications
of abrasive grits, covered by U.S. Pat. No. 3,181,939, but cooled
to produce alumina crystals of 20 - 30 microns or less, as
described in U.S. application Ser. No. 98,014 filed Dec. 14, 1970,
which issued as U.S. Pat. No. 3,781,172 on Dec. 25, 1973, (Pett and
Kinney). While Minnesota Mining had, on a limited basis, marketed a
coated abrasive containing an alumina zirconia eutectic of blocky
grit structure under the tradename "Cubicut," alumina-zirconia
alloy-type abrasives have not been employed commercially for wide
scale use in low pressure abrasive applications prior to the
present invention. The Cubicut product had eutectic colonies
typically 100 microns or more in average width.
In the copending application of Rowse and Lakhani there is
described the use of the Pett and Kinney type of alumina-zirconia
crystals having a "weak" shape for the manufacture of cut-off
wheels.
In attempting to produce even finer microstructure in the abrasive
by even more rapid cooling, the abrasive of the present invention
was discovered. In accordance with the trend of earlier results, in
which more rapid cooling lead to tougher abrasives more useful than
the less rapidly cooled materials in the rough, heavy duty
applications, it was expected that the most rapidly cooled material
would follow this trend. Unexpectedly however, it was found that,
when produced at near-eutectic compositions, the new abrasive, the
subject of this application, was outstandingly useful in light duty
applications.
Variation of cooling rates and compositional limits, in accordance
with the present invention, have shown that near-eutectic mixtures
of alumina and zirconia will exhibit the newly discovered
properties only when solidified at such a rapid rate that at least
one dimension of the zirconia rods or platelets present in the
material, is on the order of 1000 - 2000 angstrom units or
finer.
Thus, it has now been discovered, that by modifying the cooling
conditions for these abrasives, and by employing a near-eutectic
composition of alumina and zirconia, an entirely new family of
abrasives can be produced having remarkable utility in low or
moderate pressure applications, both in coated abrasive and bonded
abrasive applications.
SUMMARY OF THE INVENTION
Alumina and zirconia sources are fused in an electric arc furnace
to produce an alumina-zirconia melt containing from 35 to 50%
zirconia, by weight, with total impurities being not over about 3%
exclusive of titania in solid solution with alumina and/or zirconia
and at 0.1% or below in the case of soda. Any suitable raw
materials can be employed which, after fusion, including any
purification taking place during the furnacing, result in the
desired composition. Silica and titania may also be present in
small amounts. Silica should be as low as possible (preferably
below 0.3%) but at any rate should be below 1% in the product.
Titania is less harmful than silica, and, in some cases may be
deliberately included to obtain equivalent abrasives or to produce
desired effects. Hafnia, in the amounts naturally present in
zirconia sources is not considered an impurity.
Other impurities may be present in the abrasive either as
impurities associated with the particular sources of zirconia and
alumina employed, or, as in the case of MgO and CaO, they may be
deliberately added. For some applications, the presence of CaO, up
to 2% is desirable. With MgO, at levels above 4%, the alumina in
the product is essentially all converted to magnesia deficient
spinel.
The molten alumina-zirconia is then solidified at a very rapid
rate. The very rapidly cooled product is characterized in that it
is made up of generally oriented colonies of alumina-zirconia
eutectic wherein the zirconia, when it precipitates in rod form,
has an average diameter below 2000 angstrom units near the colony
center, the zirconia rods being surrounded by an alumina matrix. A
preferred composition is one (e.g., 43% ZrO.sub.2) in which the
primary alumina may crystallize first as a seed for the eutectic
crystallization, the orientation of which is at least initially
controlled by the orientation of the alumina seed. The eutectic
crystallization is a simultaneous crystallization of alumina and
zirconia according to the eutectic ratio. The combined seed and
eutectic oriented mixture become an individual cell or colony on
which the trigonal outline of the seed crystal may sometimes be
visible. The colonies have dimensions of up to 60 microns,
typically 5 to 60 microns, with a typical average cross-sectional
dimension of less than 30 to 40 microns when observed in
thin-sections or polished sections. They are usually grouped in
granular formations consisting of a number of neighboring similarly
oriented elongated, eutectic colonies with their long axes
generally perpendicular to the cooling surface. The crystal form of
the zirconia in such products preferably has as much as 25% or more
of the zirconia in the tetragonal crystal form, which is,
ordinarily, stable only at temperatures above 1000.degree.C.
In the preceeding discussion of the size of the zirconia "rods" in
the alumina zirconia eutectic colonies reference has been made to
rod diameter. Measurements of the rod diameter have been achieved
by direct scaling of scanning electron microscope photographs with
magnifications of 5,000.times. to 10,000.times.; in some cases
magnification of 20,000.times. has been used. Since the diameters
of the zirconia rods generally increase from the center of the
eutectic colonies to the outer edges of the colonies, it is
preferred to make the measurements near the center of the colonies.
This is also believed to be the most useful measuring technique in
characterizing the colonies since the growth rate in various
portions of the periphery of the colonies may be different (due to
geometrical effects) and therefore the rod diameters and rod
spacings will be different. Additionally, impurities will
congregate at the edges of the colonies and this will also disrupt
the rod spacings and rod diameters, thus giving dimensions which
are generally considerably larger than the dimensions near the
center of the colonies. We believe that the abrasive properties of
the eutectic-containing abrasive grits are more critically
dependent upon the dimensions at the colony centers.
While the discussion of zirconia particle size in the alumina
zirconia eutectic has been based predominantly on size
characterization of rods there is strong evidence that in addition
to rods being present a substantial portion of the zirconia is in
the form of platelets, these platelets having a thickness of the
same order as the rod diameters. In some of the early work wherein
rods were identified in scanning electron photomicrographs, further
analysis of such samples indicates that these rods were in fact
platelets. This determination was made by etching the alumina from
the region of the zirconia alumina eutectic colony and reexamining
the etched sample under a scanning electron microscope.
In the preceeding discussion the rod diameter has been referred to
as an important parameter to be measured. As a practical matter it
is probably better to use rod spacing as the measured parameter
rather than rod diameter, since rod spacing is not as critically
dependent upon the resolution of the electron microscope. This is
particularly true where the rod appears to have a fuzzy edge and it
may be difficult to precisely determine the actual diameter to be
measured. However, the spacing between two (2) rods or two (2)
platelets having fuzzy edges can be quite accurately measured by
measuring the distance between the centers of the two rods or
platelets. The rod spacing and rod diameters are directly related
by the following approximate equation: ##EQU1## Wherein d.sub.1 is
the distance between the centers of adjacent rods, d.sub.2 is rod
diameter and V.sub.f is the volume fraction of zirconia.
Platelet spacing and platelet thickness are also directly
related.
In the measurement of rod (or platelet) spacing a convenient method
to use is the random intercept technique which consists of drawing
a straight line (real or imaginary) across a photomicrograph of the
area where the rod spacing is to be measured, this line being
normal to the rod axis or platelet plane. The number of rods or
platelets intercepted by the line are then counted over a given
distance to obtain the average rod or platelet spacing.
Another observable characteristic of the abrasive of this invention
is the association of groups of colonies having similar
orientation. Such groups of colonies, following the terminology of
the metallurgists, are referred to as grains. Such grains may
typically include from 2 to 100 or more colonies. Analysis by the
electron microprobe shows that the great bulk of the impurities
(95% or more) appears in the boundaries between colonies and
between grains. The boundary material consists of the impurities in
glassy and crystalline forms and may include elemental metals, and
combinations of the metals with oxygen, carbon, and nitrogen.
Aluminum and zirconium are also found in combined forms in the
boundary phases. The colonies are essentially alumina and zirconia
which may contain TiO.sub.2 or other material in solid solution
without adversely affecting its hardness or strength.
Abrasive grits, resulting from crushing the solidified abrasive,
contain a plurality of colonies or cells and, depending upon their
size may contain a plurality of grains. Useful commercial grit
sizes range from about 6 grits to 180 grit size, and finer as
defined by conventional grit sizing as, for example by the U.S.
Department of Commerce Commercial Standard CS 271-65, issued Apr.
12, 1965.
The generally parallel orientation of associated elongated colonies
and grains referred to previously, is believed to create the unique
fracture characteristics of material of this invention which is
particularly suited for use in coated abrasives. This new type of
fracture provides continuous "sharpening" of the fractured grains
by exposing new cutting edges, thereby prolonging the useful life
of the abrasive. Such fracture, a major portion of which takes
place along colony and grain boundaries results in striated or
columnar surfaces along the plane of fracture parallel to the long
axes of the colonies, and a stepped surface for fractures
perpendicular to the axis of the colonies. When examined under a
microscope with relatively small magnification the edges defined by
intersection of two planes of fracture are discontinuous, jagged,
and sharp. Also observable in some fractures is a jaggedness and
irregularity in the columnar structure apparently resulting from
slight misalignments of colonies in adjacent grains.
For the purposes of this application, the type of fracture
described above and exhibited by grain particularly suited for
coated abrasive applications is referred to herein as
"pseudo-hackly" to distinguish from the term "hackly" as used by
mineralogists in describing a somewhat different fracture exhibited
by minerals (single crystal, or sometimes polycrystalline,
compounds or elements) as distinguished from the composite
(eutectic), finely crystalline, abrasive materials of this
invention. When a large portion of the abrasive sized grits in a
given batch of material of this invention exhibit the pseudo-hackly
fracture described above, the abrasive is particularly suited to
coated abrasive applications.
It has also been observed that in the abrasive material produced in
pours of several hundred pounds, the material is normally not
entirely homogenous and may contain grits which exhibit the
presence of primary (non-eutectic) alumina crystals, grits which
exhibit primary zirconia crystals, and grits which are essentially
all-eutectic, with no evidence of primary crystals. Material which
contains 50% or more of the all-eutectic grits is particularly
preferred for coated abrasive applications. To determine the "%
all-eutectic" grits the material is crushed to abrasive sized grits
and polished sections are examined under an optical or scanning
electron microscope. Those grits indicating the presence of primary
alumina or primary zirconia crystals at this magnification are
considered not to be all-eutectic and are subtracted from the total
number of grits in the sample to determine the numerical %
all-eutectic grits.
In preparing the abrasive grits of this invention the cast material
is crushed and screened to obtain the desired grit sizes. Initial
rough crushing may be by jaws or impact as conventional in the
industry. Thereafter rolls crushing is desirable to produce more
friable, elongated particles as may screening through slotted
screens, depending upon the desired final grit form. By use of
these techniques on the unique eutectic composition of the present
invention an abrasive grit having a "weak" shape can be
provided.
The abrasive grit of this invention, when the fusion conditions are
reducing such that reduction products such as carbides, suboxides
or metal inclusions are present in the cooled product is sensitive
to heat, and prolonged heating above 500.degree.C in
oxygen-containing atmospheres results in cracking and weakening of
the grit. Irreversible impairment of the grinding properties takes
place during such heating making it entirely unsuitable for use in
bonded or coated abrasives. The change appears to involve a change
in the chemistry of the boundary phase material and is associated
with an increase in oxygen content of the abrasive. In the
manufacture of abrasive articles from such grit (although grit
produced under reducing conditions may be preferred for coated
abrasive purposes) it is necessary to avoid prolonged heating of
the grit above 500.degree.C in the presence of oxygen and heating
of the grit at or above 1250.degree.C even in the absence of oxygen
may be undesirable.
The deleterious effect of prolonged heating is largely eliminated,
however by using no carbon or a minimum of carbon in the furnacing
operation, or by producing oxidizing conditions such as by an air
or oxygen purge of the molten abrasive prior to casting. Such
products have been typically found to contain 0.5% or less carbon.
Products thus "oxidized" or produced under minimal reducing
conditions are found however to be less preferred for coated
abrasive use. For coated abrasive uses best results have often been
achieved where excess carbon is employed resulting in a dark
colored grain in which some reduction products such as carbides,
nitrides, or metals are present as evidenced by visual
examination.
Convenient methods for achieving the rapid cooling necessary to
produce the improved abrasive of this invention are the use of
metal balls such as described in the copending application of John
K. Shurie, Ser. No. 112,715 filed Feb. 4, 1971, or by pouring the
melt between metal plates, as described in the copending
application of Scott Ser. No. 212,614 filed Dec. 27, 1971. Air
quenching is also possible by pressure atomization in air of the
molten abrasives into small spheres having a diameter in the order
of 1000 microns and finer. Such air quenched abrasive has somewhat
different properties from poured molten materials and does not
suffer from subsequent heating in oxygen to the degree shown by the
poured materials.
EXAMPLE I
A mixture for fusion in the electric arc furnace was made up of 60
parts by weight of E-286 alumina (fused low soda alumina) with
441/4 parts of zirconia, and 1/2 part barley coal. The zirconia
typically contained 2 to 3% hafnia and 12 of the 441/4 parts
consisted of fused zirconia (Q5AlO) having the following typical
analysis by weight:
Al.sub.2 O.sub.3 9.8% (by difference) SiO.sub.2 5.24% Fe.sub.2
O.sub.3 0.14% TiO.sub.2 0.24% CaO 0.24% MgO 0.12% ZrO.sub.2 84.2%
(including hafnia)
with the remaining 321/4 parts of zirconia (Ql) having the
following analysis by weight:
SiO.sub.2 0.56% Fe.sub.2 O.sub.3 0.10% TiO.sub.2 0.26% CaO 0.12%
MgO 0.03% Al.sub.2 O.sub.3 0.46% ZrO.sub.2 98.5% (including
hafnia).
A fusion was made in the conventional manner in an arc furnace
arranged for pouring of the molten contents. The four cubic foot
furnace employed two 4 inch diameter graphite electrodes, spaced
eight inches apart (center to center) and was operated at 85 volts
and 175 kilowatts. The average feed rate was 175 to 200 pounds an
hour. The product was poured into a cast iron ingot mold filled
with 1 inch diameter steel balls. A total of 1712 pounds of
material was cast in a series of pours. The average analysis of the
composite product made from a number of similar runs was:
Na.sub.2 O 0.04% SiO.sub.2 0.24% Fe.sub.2 O.sub.3 0.13% TiO.sub.2
0.13% ZrO.sub.2 39.85% Al.sub.2 O.sub.3 59.61% (by difference).
The small amount of hafnia is reported at ZrO.sub.2 above, and
throughout this application. The average rod diameter of the
zirconia in the center of the eutectic colonies was found, by a
scanning electron microscope, to be less than 2000 angstroms, with
a minimum diameter of below the resolution (300 A) of the
microscope, the larger diameter rods being found only in small
amounts at the slowest cooled portions of the product (furthest
removed from the ball cooling surface). The average rod spacing at
the colony centers was typically less than 4000 angstroms and the
platelet spacing was similar. The average platelet thickness was
less than 2000 angstroms at the colony centers.
In the parent applications the average rod diameters were reported
as being somewhat smaller than the values given here. These earlier
averages were based on the assumption that a substantial portion of
the rods had sufficiently small diameters (less than 300 A) as to
be unresolved by the scanning electron microscope; this assumption
being based on the reported maximum diameter of 300 A for
tetragonal zirconia. It is now believed that zirconia rods having a
size much greater than 300 A can give an X-ray diffraction pattern
indicative of the tetragonal form.
The zirconia was 31% in the tetragonal form, the remainder
monoclinic, as determined by measurement of the angular position of
the centroid of the powder X-ray diffraction pattern, for the
monoclinic doublet peak and the tetragonal peak; at about
30.3.degree. (2 theta), for the tetragonal peak and at about
28.3.degree. and 31.5.degree. for the monoclinic doublet, when
copper K radiation is employed. The centroid of the
monoclinic-tetragonal triplet is determined by conventional
mathematical procedures after the profile of the triplet has been
determined by careful counting, the probable counting error being
of the order of 2.5% or better. The weight percent of tetragonal
can then be read from a calibration curve, based on the following
parameters:
Area (integrated intensity) of monoclinic doublet, A.sub.m = 72.73
arbitrary units
Area (integrated intensity) of tetragonal peak, A.sub.t = 84.79
arbitrary units
Position of monoclinic doublet, X.sub.m, (measured from
27.00.degree.) = 2.500.degree.
Position of tetragonal, X.sub.t, (measured from 27.00.degree.) =
3.266.degree.
These parameters were obtained from known samples containing 100%
tetragonal and 100% monoclinic zirconia forms. It will be
understood that specific values for area and position of peaks in
the X-ray tracing will vary somewhat depending upon the
instrumental set-up and the quality of the samples used. In the
case of tetragonal zirconia the sample was 40% zirconia and 60%
alumina. From the mass absorption coefficients it can be calculated
that the true intensity of the monoclinic peak in the presence of
60% alumina is 0.58 times the measured integrated intensity, giving
a true relative value of 72.73 units. A calibration curve can be
obtained, where X.sub.3 is the angular position (measured from
27.00.degree.) of the centroid, and w is the weight fraction of
tetragonal zirconia, from the following relation: ##EQU2## which
relates X.sub.3 to any given value of w from 0 to 1. Thus for any
value of X.sub.3, determined from a given X-ray diffraction
pattern, the corresponding value of w can be calculated or read
from the calibration curve. It is in this way that all of the
values for percent tetragonal given herein were obtained. We have
found that a cooling rate fast enough to cause at least 25% of the
zirconia to be in the tetragonal form is necessary to produce the
abrasives of this invention. It has also been found that the
crystalline form of Al.sub.2 O.sub.3 known as delta-alumina is
contained in samples which include tetragonal zirconia, the amount
of delta-alumina increasing as the tetragonal zirconia content
increases. In air quenched material containing 100% tetragonal
zirconia we have found that essentially all of the alumina appears
in the delta-form, as determined by standard powder X-ray
diffraction; however the amount of delta alumina is not believed to
be proportional to the percent tetragonal zirconia since some
analytical x-ray analyses of samples containing up to 40%
tetragonal zirconia indicated that essentially all of the alumina
was in the alpha form.
The product of Example I was passed through a 20 inch by 6 inch jaw
crusher to yield a product 1/2 inch and finer in size. The 1/2 inch
product is then further crushed by rolls or impact to yield the
desired grit sizes for use in bonded or coated abrasives. The
abrasive yields superior results in medium and light duty
applications. The abrasive grits were largely (51%) pseudo-hackly
and predominantly (69%) all-eutectic.
EXAMPLE II
A fusion run similar to Example I was made employing a mix made up
of 60 parts by weight of a fused low soda alumina material and
423/4 parts by weight of the higher purity zirconia material of
Example I. Three casting methods were employed; 1160 pounds of
product was cast on 1 inch diameter steel balls, 205 pounds was
cast on 5/8 inch steel balls, and 120 pounds was cast between steel
plates, spaced 3/16 inches apart. The analysis of the product
was:
SiO.sub.2 0.18% Fe.sub.2 O.sub.3 0.13% TiO.sub.2 0.13% ZrO.sub.2
40.40% Na.sub.2 O 0.05% Al.sub.2 O.sub.3 59.11% (by
difference).
The crushed abrasive was employed to make grinding wheels for test.
The bond in the wheels was 75% by weight of powdered two stage
phenol-formaldehyde resin (Union Carbide BRP5417) and 25% barium
sulfate filler. In making the wheels the abrasive grains were wet
with a one stage liquid phenolformaldehyde resin and mixed with the
powdered resin (which contained 8 - 9% hexamethylenetetramine), and
filler. Two grades of wheel were made by cold pressing to stops in
a mold and curing conventionally with an upper temperature limit of
175.degree.C, one containing 54% abrasive, 22% bond, and 24% pores,
and the other containing 54% abrasive, 26% bond, and 20% pores (all
by volume). A similar set of wheels using standard fused alumina
was prepared for comparison in foundry snagging employing a
standard portable grinder.
The test employed a pneumatic straight grinder, 5900 revolutions
per minute wheel speed. The wheels were six inches in diameter, and
one inch thick. The workpiece was a cast steel cylinder, 12 inches
outside diameter by 103/4 inches inside diameter, mounted on a
rotary table at 12 revolutions per minute. The grinding pressure
(between the wheel and the 5/8 inch wall surface of the work) was
26 pounds. The wheel wear (W) in cubic inches per hour, pounds of
metal removed from the workpiece (M), and grinding ratio (G),
pounds of metal removed per cubic inch of wheel wear, are reported
below for the standard wheels and the test wheels.
______________________________________ Wheel W M G
______________________________________ Standard (22% bond) 9.07
7.33 2.9 Standard (26% bond) 7.16 6.82 3.4 Test (22% bond) 4.49
7.70 6.0 Test (26% bond) 4.19 7.55 6.4
______________________________________
As can be seen from the data, the softer test wheel was more than
twice as efficient as the standard wheel, while the harder wheel
was not quite (1.89X) twice as efficient as the harder standard
wheel. This illustrates the unexpected advantage of the new
abrasive under mild (lower pressures, softer wheels) grinding
conditions.
The abrasive in this test was first jaw crushed, as in Example I,
then impact crushed to produce through 6 mesh on 24 mesh grits, and
the through 6 on 10 mesh fraction of the grits was then rolls
crushed and screened to produce a 24 grit size for use in making
the wheels. Essentially equivalent results can be achieved by
substitution of jaw and/or rolls crushing for the impact crushing
step. The standard wheels employed regular fused rolls-crushed
alumina made by fusing bauxite and having a typical analysis of 95%
or more Al.sub.2 O.sub.3 with the remaining 5% or less being made
up of mainly silica, iron, and titania.
The material of Example II which was cast on 5/8 inch balls was
somewhat finer in microstructure than the 1 inch ball cast material
and had a higher tetragonal zirconia content. The material cast
between steel plates had an average zirconia rod diameter of less
than 1500 angstrom units and the colony cross-sectional diameter
measured 10 to 30 microns on polished sections. In this method of
casting the molten abrasive is poured on the top of a plurality of
spaced vertical steel plates, each plate being 1/2 inch or more
thick, spaced (for example) 3/16 inches apart. The product is
recovered from the spaces between the faces of the plates. Its
tetragonal zirconia content is 46%, and its grinding properties are
excellent. The grits were 60% psuedo-hackly and 77%
all-eutectic.
EXAMPLE III
The furnace mix consisted of 60 parts by weight of fused low silica
alumina, and 423/4 parts of the higher purity zirconia employed in
Example I.
The mix was fused in the conventional manner employing an average
of 175 kilowatts at an average of 85 volts. Product in the amount
of 315 pounds, poured on 1 inch steel balls was recovered. The
average analysis of the product was:
SiO.sub.2 0.17% Fe.sub.2 O.sub.3 0.15% TiO.sub.2 0.13% ZrO.sub.2
38.09% CaO 0.09% MgO 0.02% Na.sub.2 O 0.03%
The alumina is determined by difference in this case to be 61.32%.
The impurities are present, essentially, in the colony and grain
boundaries. (The product was 57% pseudo-hackly and 71%
all-eutectic.) Although the constituents are all reported on the
analysis as oxides, some carbides, oxycarbides, nitrides,
carbonitrides, oxynitrides, suboxides, and sometimes elemental
metal are ordinarily present in the boundary material. Analysis of
typical product has shown about 0.1% nitrogen and 0.02 to 0.1%
carbon. This can also be demonstrated by the weight gain of the
material when subjected to oxidation conditions. It is believed
that a portion of this weight gain is due to the uptake of oxygen
by non-stoichiometric zirconia in the colonies proper. Where
elemental metals or carbon and nitrogen compounds are absent, some
weight gain will still be observed.
EXAMPLE IV
Bayer process alumina and baddeleyite were employed in the ratio of
44.4 parts of baddeleyite to 60.5 parts of bayer process alumina,
with 2 parts of barley coal, and the fused mixture was cast on 1
inch steel balls. The average product analysis was as follows:
SiO.sub.2 0.11% Fe.sub.2 O.sub.3 0.2% TiO.sub.2 0.36% ZrO.sub.2
40.36% Na.sub.2 O 0.08% Other: about 0.08% (CaO, MgO etc.) Al.sub.2
O.sub.3 58.2%
The baddeleyite employed as the source of ZrO.sub.2 had the
following typical analysis:
SiO.sub.2 0.63% Fe.sub.2 O.sub.3 0.53% TiO.sub.2 0.67% CaO 0.63%
MgO 0.70% ZrO.sub.2 96.8%
The wheels were phenolic bonded and included standard commercial
fillers. The abrasive grits of this example were 54% pseudo-hackly
and 61% all-eutectic. For use in cut-off wheels the grits are
preferably impact crushed to a strong shape.
This product of Example IV gives a 400 to 500% increase in
efficiency in cut-off wheels, as compared to the best known
commercial aluminum oxide cut-off wheel in cutting ductile iron at
relatively light pressure, using a 20 horse power standard
commercial cut-off machine, operating chopper style on 11/8 inch
cross section workpieces.
EXAMPLE V
Impact crushed (-6, +16), 40% by weight zirconia abrasive grit
material, manufactured as in Example I, was rolls crushed in
conventional fashion. The crushed abrasive material was then
screened, (to separate out for use those abrasive grains having a
grit size 36 as defined in P.S. 8-67, U.S. Department of Commerce)
and the screened material was then washed with water. Next, the
abrasive material was subjected to a magnetic field to remove any
magnetic particles therefrom.
To a 30 mil vulcanized fiber backing member (10 inches .times. 11
inches) was applied (28.6 pounds per sandpaper maker's ream) a
maker adhesive having the following composition:
Components Weight ______________________________________ 1) Liquid
resin No. 1, a phenol-formaldehyde resol resin, having a
formaldehyde to phenol ratio of 1.7 to 1, caustic catalyzed, with a
solids content of 73%. 1644 grams 2) Liquid resin No. 2, a
phenol-formaldehyde resol resin, having a formaldehyde to phenol
ratio of 0.94 to 1, caustic catalyzed, with a solids content of
78.4%. 650 grams 3) CaCO.sub.3 (14 micron) 3300 grams 4) Water 165
grams to - give a viscosity at 100.degree.F of 8000 centipoise
______________________________________
Upon the maker adhesive was then electrocoated, according to usual
techniques for upper propulsion, the zirconia-alumina abrasive grit
above-mentioned. The amount of abrasive grit deposited was 59.0
pounds per sandpaper maker's ream. The thus coated backing member
was then heated for 45 minutes at 140.degree.F, 45 minutes at
175.degree.F, 60 minutes at 220.degree.F, and 90 minutes at
250.degree.F.
A size coat composition was then applied to the abrasive grit -
maker adhesive surface, such being of the same composition as the
maker adhesive except that water has been added thereto (200 grams
H.sub.2 O) to provide a more dilute composition. This composition
was applied in sufficient amount to provide a size coat of 27.0 -
29.4 pounds per sandpaper maker's ream (wet weight). Drying and
curing was obtained in heating the coated substrate material for 45
minutes at 115.degree.F, 60 minutes at 150.degree.F, 45 minutes at
175.degree.F, 45 minutes at 200.degree.F, 180 minutes at
225.degree.F, and 45 minutes ata 235.degree.F.
The coated abrasive material thus manufactured was then humidified
at 50% R.H., 70.degree.F overnite after which a 7 inch diameter
disc was die-cut therefrom for evaluation. Prior to evaluation, the
abrasive disc was curl corrected according to usual techniques by
double flexing, one flex being in a direction perpendicular to the
other.
EXAMPLE VA
The abrasive disc in Example V was evaluated in a mechanical disk
tester on 1020 LC steel. In this machine, a workpiece (1/8 inch
.times. 1 inch .times. 1 inch .times. 93/4 inch angle iron)
oscillates back and forth at a rate of 7 feet per minute over a
distance of 93/4 inches, the 1/8 inch face being ground with the
abrasive disc rotating at a speed of 3450 RPM. A force of 12 pounds
is maintained against the workpiece by a phenolic back-up pad. The
face of the disc was at a 10.degree. angle with the surface being
ground.
The performance of the disc of this invention was compared with a
similar abrasive product except that the abrasive grain material
thereon was of conventional high purity alumina. Over a 10 minute
period, the coated abrasive disc of this invention cut 166% that of
the control abrasive disc.
EXAMPLE VB
An abrasive disc manufactured as in Example V was evaluated in the
machine disclosed in Example VA except that a workpiece of 304
stainless steel was utilized and the abrasive was maintained
against the work with a force of 10 pounds.
The coated abrasive material of this invention in 6 minutes cut
154% that of a control disc of conventional high purity
alumina.
EXAMPLE VC
Zirconia-alumina abrasive grain material (40% ZrO.sub.2) which was
manufactured as described in Examples I and II (1 inch ball cast)
was jaw crushed to 1/2 inch chunks. This abrasive material was then
rolls crushed to 36 grit size, screened, washed with water, and
purged of magnetic particles.
A conventional resole phenol-formaldehyde maker adhesive
composition was prepared by mixing together the following:
Components Weight ______________________________________ Varcum
Resin 2535 (a resol having 18 pounds a solids content of 78%, a
formaldehyde to phenol ratio of 2.01 to 1, caustic catalyzed and
modified with di-propylene glycol Number 2 liquid resin of Example
V 7.5 pounds CaCO.sub.3 (14 micron) 31.0 pounds H.sub.2 O 2.25
pounds RMR Pontamine brown dye (Dupont Co.) 24 grams
______________________________________
This composition (100.degree.F, viscosity 7000 c.p.s.) was coated
on the front side of a cotton drills woven backing member (7
oz./yd.sup.2) having a 2 .times. 1 twill construction, a yarn count
of 76 in the warp and 48 in the fill directions, yarn numbers of
12s cotton warp and 17s fill, which had been provided with a
conventional glue-starch finish. Sufficient composition was
deposited on the backing member to provide, on drying and curing, a
maker adhesive coat of 21 lbs. per sandpaper maker's ream.
Subsequent to application of the maker adhesive composition,
reclaimed abrasive (high purity alumina, 36 grit) was gravity
coated (20.8 lbs. per sandpaper maker's ream) on the layer of
adhesive composition. This abrasive-adhesive coated backing member
was then heated at 170.degree.F for 25 minutes, 190.degree.F for 25
minutes and 225.degree.F for 47 minutes. A second maker adhesive
coat was then provided on the backing member, (22 lbs., dry weight,
per sandpaper maker's ream), being of the same composition as the
first maker coat, upon which was then electrostatically deposited,
in conventional fashion, 38.6 lbs. per sandpaper maker's ream of
the above-described zirconia-alumina abrasive grit. The
abrasive-adhesive coated backing member was then heated as before
described.
A size adhesive composition was prepared of the same components as
the maker adhesive except that sufficient water was added tehreto
to provide a composition having a viscosity of 1100 c.p.s. at
100.degree.F. After application of the size composition, the thus
coated backing member was heated at 125.degree.F for 25 minutes,
135.degree.F for 25 minutes, 180.degree.F for 18 minutes,
190.degree.F for 25 minutes and 230.degree.F for 15 minutes.
Sufficient size composition was provided to result in a wet weight
of 28 lbs. per sandpaper maker's ream. The abrasive-adhesive coated
backing member was then given a final cure by heating it for 8
hours at 230.degree.F after which it has ready to be manufactured
into abrasive articles for various applications.
EXAMPLE VD
Coated abrasive material manufactured as in Example VC (rubber roll
standard single flexed) was slit into appropriate lengths and
widths and made, according to usual techniques, into endless
abrasive belts (21/2 inches .times. 60 inches). The belts were then
evaluated under controlled conditions in a so-called "backstand
belt test" wherein, in general, a belt, positioned horizontally, is
moved inwardly at a constant pressure and in a direction
substantially normal against the 1/2 inch face of a workpiece (1/2
inch .times. 2 inches .times. 93/4 inches) moving back and forth
over a distance of 93/4 inch at 7 feet per minute. In this test,
the abrasive belt was driven at 5000 surface feet per minute (SFPM)
over a 55 durometer, rubber, vertically disposed, serrated contact
wheel (7 inches diameter) with 15 lb. dead weight exerted on a
workpiece of A-6 steel.
For purposes of comparison, a control belt of conventional high
purity alumina was evaluated in the back stand test in the same
manner. The coated abrasive material for the control belt was
manufactured as above-described, i.e., a double coat coated
abrasive material, except that the weight of abrasive grit (1900
ALUNDUM - high purity alumina) applied in the second coat was 39.9
lbs. per sandpaper maker's ream. The results are tabulated
below:
Belt Time (Min.) Cut Grams ______________________________________
Control 40 677 Zirconia-alumina 40 1235 120 2350
______________________________________
As indicated by the data, the control belt gave out after 40
minutes and a cut of only 677 grams. However, over the same time
period, the belt in accordance with the invention cut 1235 grams
(approximately 180% that of the control belt). Moreover, this belt
cut for 120 minutes before giving out, the total cut being 2350
grams.
EXAMPLE VE
Abrasive belts as in Example VD were evaluated as described therein
except that the workpiece was 304 stainless steel and the belt
speed was 3000 SFPM. In a time-end test of 30 minutes, the control
belt cut 140 grams; however, the abrasive belt of this invention
cut 178 grams
EXAMPLE VF
Abrasive belts as in Example VE were evaluated in the backstand
belt test except that, for purposes of comparison, the grinding
operation was performed using Stuart's THREAD-CUT No. 99, a
sulfur-chlorinated oil, as a grinding lubricant. A 30 minute test
resulted in a control belt cut of 145 grams. By comparison, the
abrasive belt utilizing the zirconia-alumina abrasive grain of this
invention cut 279 grams.
EXAMPLE VG
The abrasive grit material like that of Example II, 1 inch ball
cast, was rolls crushed, as before described in Example V to 36
grit, and was used in the manufacture of abrasive discs as
described therein. Discs so manufactured were evaluated in the
mechanical disc tester and under the same conditions as
before-mentioned for the respective type workpieces. The results
are indicated below.
Disc Time Min. Workpiece Cut %
______________________________________ Control* 10 1020 LC Steel
100 Zirconia-alumina 10 do. 155 Control 6 304 s.s. 100
Zirconia-alumina 6 do. 162 ______________________________________
*Control discs contained conventional high purity alumina
abrasive.
EXAMPLE VH
A fusion containing approximately 40% zirconia was poured between
steel plates spaced 3/16 inches apart. The average analysis of the
product was:
SiO.sub.2 0.21% Fe.sub.2 O.sub.3 0.15% TiO.sub.2 0.15% ZrO.sub.2
40.56% Na.sub.2 O 0.04% Al.sub.2 O.sub.3 58.89% (by
difference).
No analysis was made for the small amounts of lime or magnesia
which were present.
Discs of abrasive material, manufactured as described in Example V
except that the abrasive grain material was that described above
were evaluated grinding workpieces of 1020 L.C. steel and 304
stainless steel. The results were comparable to those obtained in
Example VG. The discs manufactured using the zirconia-alumina
abrasive material cut 162% better than the control (high purity
alumina) in the case of 1020 L.C. steel and 154% better than the
control in the case of 304 stainless steel.
EXAMPLE LJ
Coated abrasive material was manufactured as before-described in
Example VC. The abrasive (36 grit) utilized in this material was
that described in Example VH.
Abrasive belts were manufactured according to usual techniques and
these belts were tested, as before-described, in a backstand belt
test. The same conditions were used in Example VD. The results are
indicated below for the various workpieces. The test were conducted
dry except where indicated.
Time Cut Belt Workpiece Min. Grams Cut %
______________________________________ Control* 1018 L.C. 30 591
100 Steel Zirconia-alumina 1018 L.C. 30 1410 -- Steel 60 2027 343
Control 304 Stainless 30 133 100 Steel Zirconia-alumina 304
Stainless 30 222 167 Steel Control 4130 Steel 60 1050 100
Zirconia-alumina 4130 Steel 60 2215 211 Control** 1018 16 208 100
Zirconia-alumina** 1018 16 455 -- 40 728 350 Control** 304 30 153
100 Zirconia-alumina** 304 30 358 234
______________________________________ *all control belts were of
conventional high purity alumina (36 grit) and such were
manufactured in the same manner as the belts of this invention, the
only difference being the composition of the abrasive material.
**wet grinding using THREAD-CUT No. 99.
EXAMPLE VK
A coated abrasive belt was made of the novel abrasive and compared
against a standard belt under the same conditions as in Example VC
in grinding 1018 steel.
The backing was the same as in the previous belt example, the front
finish of the cloth was a calcium carbonate filled
phenol-formaldehyde and the back size was a glue-starch combination
with no filler.
The composition of the maker adhesive was as follows:
Components Weight ______________________________________ Varcum
Resin 2535 18 pounds Liquid resin No. 2 of Example V 7.8 pounds
CaCo.sub.3 (14 micron) 31 pounds Brown Dye 21 grams Water 3 pounds,
to give a viscosity of 5000 centi- poises at 100.degree.F.
______________________________________
The maker weight applied was 22 pounds per sandpaper maker's ream
for the control and 22.6 pounds for the experimental item. The
abrasive was a 40% zironia, cast on 1 inch steel balls, jaw and
rolls crushed to 36 grit. The abrasive was electrostatically
upwardly propelled in an amount of 58 pounds per sandnpaper maker's
ream for the control, and 57.8 pounds for the experimental
abrasive. The size coat was the same as the maker coat, but diluted
to 1100 centipoise at 100.degree.F, and was applied in the amount
of 28 pounds per sandpaper maker's ream (wet weight). The
abrasive-adhesive coated backing was heated for 25 minutes at
107.degree.F, 25 minutes at 190.degree.F, and 47 minutes at
225.degree.F, prior to application of the size coat. After sizing,
the cure was 25 minutes at 125.degree.F, 25 minutes at
135.degree.F. 18 minutes at 180.degree.F, 25 minutes at
190.degree.F, and 15 minutes at 230.degree.F, following by 8 hours
at 230.degree.F.
The test conditions were the same as in Example VD, employing 1018
steel as the workpiece. After 40 minutes the standard control
abrasive was used up, having removed 886 grams of steel. After 40
minutes the abrasive of this invention had cut 2196 grams and was
used for an additional 32 minutes to give a total metal removal of
2912 grams in 72 minutes.
EXAMPLE VL
Belts were prepared employing standard fused alumina, double
coated, to provide the standard. The test belt, employing abrasive
grits of the present invention, employed the standard fused alumina
undercoat, with the second coat being alumina-zirconia grain such
as employed in the previous example.
The backing material was the same as in Example VC; the maker coat
was the same as in Example VK. The maker adhesive was applied in
the amount of 27.4 pounds per sandpaper maker's ream, for both the
control and the test material. The first abrasive coating was
applied by gravity in the amount of 35.2 pounds per ream. The
second grit coating was 21.8 pounds per ream for the control, and
17.8 pounds per ream for the experimental. The size coat was
applied in the amount of 28 pounds (wet) per ream and was the same
composition as in Example VJ. The heating and curing cycles were
also the same.
Under the same test conditions as the previous examle, for a time
of 16 minutes, the control removed 310 grams of 1018 low carbon
steel, while the test abrasive removed 494 grams.
For additional comparison of the abrasive of this invention with
high quality abrasive of fused alumina, especially manufactured to
use iin precision grinding, special resinoid (phenolic) bonded
wheels were made up by hot-pressing and curing a mix containing 32%
by volume of abrasive and 68% by volume of a two stage powdered
phenol-formaldehyde resin (including, in the resin, 30% of 600 grit
alumina powder as a filler). In forming the mix a small amount of
furfural is employed to wet the abrasive grits.
The wheels were straight wheels, ,5 inches in diameter by 3/16
inches thick with a 11/4 inch center hole. The grinding section was
a 1/8 inch thick rim and was molded onto a preform to produce the
wheel. The grinding operation was fixed feed wet surface grinding.
The wheel speed was 5300 surface feed per minute; the table
transverse was 50 feet per minute; the unit crossfeed was 50 mils;
the unit downfeed was 1 mil; the materials ground were Huron (D3)
die steel (Rockwell C hardness 55), and 1045 mild steel (Rockwell b
hardness 89), 2 inches wide by 16 inches long. The total downfeed
was 20 mils per run, 1 run per wheel; the coolant was water with
corrosion inhibitiors.
The control abrasive was high purity fused alumina crystallized
from an aluminum sulfide matrix, as described in U.S. Pat. Re No.
20,547, and sold by Norton Company, Worcester, Massachusetts, under
the designation 32 ALUNDUM. This type of abrasive is free of
thermal strains, is essentially monocrystalline and, in this type
of precision grinding, gives as high grinding ratios any known
commercially available aluminum oxide abrasives.
The average value for G ratio for the control abrasive was 15.7
volumes of metal removed per volume of wheel wear for the mild
steel. The near-eutectic zirconia alumina of this invention, poured
between 3/16 inch spaced steel plates gave a G ratio of 29 in
grinding the MS steel. In both cases 60 grit size abrasive was
employed. Material of the invention cast on 1 inch balls gave an
average G value of 24 for 13 test wheels.
For D3 die steel, the G values were 4.0 for the control and 6.7 for
the abrasive of this invention, poured between 3/16 inch spaced
steel plates. For 1 inch ball cast material it was 4.6.
Such tests also show the effect of impurities, indicating that the
soda content of the abrasive should be 0.1% or lower, by weight.
Peak performance has been found with a zirconia content of 38 to
44%, with highest performance at 40.5 to 43.2%. Good results are
achieved in the range of 35 to 44%, and zirconia contents as high
as 50% are accetable. A sample containing 68% zirconia was
unacceptable in precision grinding.
EXAMPLE VI
A series of castings of abrasive material were made from a few
melts having the following general composition:
% by weight Al.sub.2 O.sub.3 58.15 (diff.) ZrO.sub.2 41.3 SiO.sub.2
0.22 Na.sub.2 O 0.02 TiO.sub.2 0.15 Fe.sub.2 O.sub.3 0.16
This molten abrasive was cast into a number of different types of
molds as described below:
50 lb. ingot mold - a cast iron mold having an interior mold cavity
8 inches by 18 inches by 9 inches. s
25 lb. ingot moldl - a cast iron mold having an interior mold
cavity 51/2 inches by 131/2 inches and 41/2 inches.
lump cast - a cast iron mold 8 inches by 18 inches by 9 inches
filled with 3/4 inches lumps of abrasive grain having essentially
the same composition and crystal structure as the material reported
as 7920 in Tables 1 and 2 under "lump cast" (the procedure of Pett
and Kinney S.N. 98,014 13/4 inch ball cast - a cast iron mold 8
inches by 18 inches by 9 inches filled with 13/4 inch diameter cast
iron balls.
1 inch ball cast - a cast iron mold 8 inches by 18 inches by 9
inches filled with 1 inch diameter cast iron balls.
3/16 inch S mold - a sheet iron mold having vertically arranged
iron partitions 3/4 inch thick spaced 3/16 inch apart.
The product resulting from the various casting techniques was then
jaw crushed in conventional fashion to 1/2 inch chunks. The chunks
of abrasive material were then rolls crushed and screened to
separate out those abrasive particles having a grit size of 36. The
screened material was then washed with water and subjected to a
magnetic field to remove any magnetic particles therefrom.
Coated abrasive material was then manufactured from the various
fused grit as in the manner described in Example VK except that the
maker adhesive used was of the composition set forth in Example VC.
The maker adhesive composition, however, contained no dye.
The backing member was the same as that described in Example VC, a
cotton drills woven fabric, and the maker weight applied was 23
lbs. per sandpaper makers ream. Abrasive grits (target weight 71
lbs./sandpaper makers ream (actual 71 + 1-2 lbs.) were
electrostatically coated onto the adhesive coated backing member in
each instance after which it was heated for 23 minutes at
175.degree.F., 23 minutes at 195.degree.F., 15 minutes at
210.degree.F., and 23 minutes at 225.degree.F. The size coat (a
less viscous maker composition) was then applied and the adhesive
coated backing member was then heated for 26 minutes at
130.degree.F., 26 minutes at 140.degree.F., 19 minutes at
190.degree.F., 25 minutes at 200.degree.F., and 15 minutes at
230.degree.F. After this the abrasive material was given a final
cure for 8 hours at 230.degree.F.
Abrasive material was manufactured in a similar manner as a control
for evaluation of the above-manufactured abrasive material except
that 1900 ALUNDUM - a high purity alumina-abrasive grit was used.
The amount of abrasive grit applied (target weight) was 61
lbs./sandpaper makers ream.
Abrasive belts were manufactured as disclosed in Example VB from
the various abrasive material provided, the belts then being
evaluated on a bench back stand belt tester as disclosed in Example
VD on 1018 steel. The results are indicated below:
Table 1
__________________________________________________________________________
Run No. Description Rate of Cut as Compared to Standard
__________________________________________________________________________
Test 1 Test 2 Test 3 Test 4 Standard 100% 100% 100% 100% 7916 50
lbs. ingot 138 134 132 131 7917 25 lbs. ingot 135 135 134 128 7920
Lump Cast 150 138 140 159 7918 13/4" ball cast 180 149 150 191 7919
1" ball cast 181 157 155 171 7921 3/16" S mold 178 148 150 189
Composite* 3/16" S mold 166 176 173 157
__________________________________________________________________________
*Mixture from a number of commercial batches
The material was also analyzed by scanning electron microscope to
determine, eutectic colony size, ZrO.sub.2 rod spacing and
ZrO.sub.2 rod size. The results were as follows:
Table 2
__________________________________________________________________________
Eutectic ZrO.sub.2 Rod and/or ZrO.sub.2 Rod and/or Colony Size
Platelet Size Platelet Spacing (Microns) (Microns) (Microns) Run
No. Description Min. Max. Ave. Min. Max. Ave. Min. Max. Ave.
__________________________________________________________________________
7916 50 lbs. Ingot 20 500 165 0.1 0.8 0.36 0.3 1.2 0.55 7917 25
lbs. Ingot 14 370 115 0.15 0.6 0.29 0.28 0.74 0.54 7920 Lump Cast 8
80 32 0.2 0.6 0.28 0.3 1.0 0.51 7918 13/4" Ball 6 100 37 0.1 0.3
0.18 0.21 0.5 0.35 Cast 7919 1" Ball Cast 6 46 22 0.1 0.25 0.15 0.2
0.5 0.29 7921 3/16" S Mold 4 44 20 0.1 0.3 0.13 0.15 0.5 0.25
Composite 3/16" S Mold 2 52 21 0.1 0.4 0.16 0.18 0.48 0.29
__________________________________________________________________________
Since the melting and pouring procedure necessarily involved
dinterrupted pouring with additions to the melt and, in some cases
different starting melts, the chemical composition of the various
runs varied somewhat as indicated below:
Table 3
__________________________________________________________________________
Run No. Composite 7916 7917 7918 7919 7920 7921
__________________________________________________________________________
ZrO.sub.2 44.22 42.86 41.33 40.73 40.69 40.60 40.55 Al.sub.2
O.sub.3 (by difference) SiO.sub.2 0.21 0.18 0.22 0.22 0.19 0.19
0.21 Na.sub.2 O 0.03 0.02 0.02 0.01 0.01 0.02 0.02 TiO.sub.2 0.20
0.15 0.15 0.16 0.15 0.16 0.14 Fe.sub.2 O.sub.3 0.11 0.10 0.16 0.18
0.18 0.16 0.17
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In addition to its use as a coated abrasive, the abrasive material
(36-60 grit) made in Example VI was also formed into grinding
wheels. These wheels were 5 inches in diameter 3/16 inch thick and
had a resinoid type bond similar to that described on page 32.
These wheels were then tested in a surface precision grinding test
of the type described on pages 32 and 33. The grinding results are
set forth below in comparison to a commercial aluminum oxide
wheel.
Table 4 ______________________________________ Grinding Ratios Run
No. Description 1045 Steel Huron Die Steel
______________________________________ 7916 50 lb. ingot 12.9 2.89
7917 25 lb. ingot 12.9 2.54 7920 Lump Cast 21.1 4.54 7918 13/4"
Ball Cast 25.0 5.36 7919 1" Ball Cast 25.2 5.37 7921 S Mold 24.0
5.03 Commercial Aluminum Oxide 20.9 3.15 (32 Alundum)
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In some other tests of grinding wheels where a lower percentage of
resin bond was employed the advantages for the new abrasive over
prior art alumina zirconia abrasives have been minimal or
nonexistent. In these other grinding wheels it is believed that the
lack of superior results was due to lack of adequate bond, thus
pointing out the dependance on the bond and bonding strength of the
wheel structure to achieve the value inherent in the abrasive. If
the bond supporting the abrasive is not sufficiently strong to hold
the abrasive while permitting gradual breakdown of the individual
grits, the self-sharpening characteristics of the pseudo-hackly
fracture along the grain and colony boundaries will not be
achieved. The requisite "bond strength" will be related to the grit
size, grit shape and grinding application.
Obvious other variations can be made in the practice of this
invention. The essential requirement as to cooling is only that the
cooling be rapid enough to achieve, in the disclosed compositions,
an average zirconia rod and/or platelet diameter of 2000 angstroms
or less, or rod and/or platelet spacing of less than 4000
angstroms.
Where used in the attached specification and claims the expression
"average" shall mean numerical average and the expression "percent"
shall mean weight percent unless otherwise indicated.
* * * * *